This invention relates to contact arrangements for vacuum switches with contacts which are movable relative to each other in general and more particularly to an improved contact arrangement.
The interruption process in vacuum switch gear is initiated by the separation of cooperating contacts at which time a metal vapor arc is produced. The shape of the contacts which are movable relative to each other is selected so that the intrinsic magnetic forces of the current to be interrupted form a force component in the azimuthal direction which sets the arc in a rotating motion so that the burn off of the contacts is limited. In the known contacts, this is accomplished by special running surfaces for the arc, which surface may form, at the same time, the seating surfaces of the contacts. The running surfaces for the arc may also surround the contact surfaces themselves and may be provided with slots so that the current paths in the contacts follow a predetermined direction. In order for the arc bases to rotate on the running surfaces, the slots generally have an approximately spiral shape relative to the axis of rotation of the contacts. However, such slots are difficult to produce.
Contact arrangements for vacuum switches which have cup shaped contacts are also known. The annular rim of the cup shaped contacts form the seating surfaces of the contacts. The outer surface of the hollow cylindrical cup is provided with slots which run in the radial direction and are inclined to the axis of revolution of the contact. In one particular embodiment of the contact, the rim of the cup is not provided with slots, so that the seating surfaces of the contacts consist of a solid annular part. The bottom of the cup which extends parallel to the seating surface, forms a sharp corner with the cylinder surface. In such cup contacts, the base of the arc can travel from the seating surface at the rim of the cup to the bottom of the cup and dwell there. The result is increased burn off of the contact material at these parts of the contact. (German Auslegeschrift 1 196 751).
The annular parts of such contacts for vacuum switches adjacent to the seating surfaces have also been provided with slots and the ring has been connected to the current leads with braces. These braces then have a conical shape. Since they are not slotted, they disturb the component of the azimuthally directed magnetic force. In addition, the fabrication of this contach is relatively difficult and its mechanical strength is limited by the braces. (Cf. Ueber die Elecktrodenerosion beim Schalten grosser Wechselstroeme im Hochvakuum (On the electrode erosion in switching large a-c currents in a high vacuum); Dissertation by F. C. Althoff, Technical University Braunschweig, 1970).